It's foolish to think that banning politicians from stock trading would do anything.
Politician Bob can always call his friend Alice to do the trading on his behalf.
People are constantly convicted of insider trading that have very remote connections with the people receiving the privileged information. The great thing about insider trading is that the trading part is public, regulators do track trading activity and suspiciously well timed trades can be investigated. It is definately not something that wouldn't have any effect.